In the production of glass fibers by a continuous process a number of individual glass filaments are drawn at high speed from an electrically heated noble metal bushing. In a typical fiber glass forming operation, molten glass from a suitable source is fed to a platinum bushing (a small container constructed of platinum or a platinum alloy). The bushing is heated electrically to maintain the supply of glass fed thereto in a molten state. The bottom of the bushing is supplied with a plurality of holes, tips or orifices through which the molten glass issues as molten streams. These streams issuing from the orifices are attenuated into fibers by drawing the streams of glass down from the bushing and winding them on a rapidly rotating forming tube. The rotation of the forming tube provides the pulling force for attenuating the glass into fibers.
In modern fiber glass manufacturing operations, the tips or orifices through which the fibers are attenuated are typically aligned in horizontal rows along the length and the width of the bottom of the fiber glass bushing. In the operation of such a bushing, heat is radiated from the bushing to the cones of glass formed as the molten glass leaves the tips and is formed into fibers. As a result, the cones of glass from which fibers are formed often cannot cool rapidly enough to form continuous fibers of uniform dimension. Viscosity in molten glass cones is low and the cones have a tendency to constrict into droplets instead of flowing as a continuous stream. This is caused by the surface tension of the glass overcoming the viscosity since the glass surface tension changes very little with temperature.
When heated bushings are employed, it has been found necessary for proper fiber formation to extract heat energy from molten cones of glass and the fibers attenuated from the apex of the molten cones of glass. This is especially necessary in larger bushings containing several rows of tips. The cooling of the cones of glass increases the viscosity of the molten glass cones and thereby eliminates constriction and droplet formation. Further, cooling of the glass cones in this manner provides for more uniform cone formation from the front to the back of the bushing in the rows of cones located in larger bushings. Uneven cone formation from a row of bushing tips located from the front to the back of a larger bushing results in uneven tension during the high speed attenuation normally associated with fiber glass formation and frequently results in breakouts. By the application of proper cooling techniques between the rows of cones, this problem is eliminated or substantially reduced.
It is well known in the art to provide means for extracting heat energy from cones of glass from which glass fibers are being drawn. Exemplary of such teachings are the teachings found in U.S. Pat. No. 2,908,036 and the method described in U.S. Pat. No. 3,251,665. In the first of these patents, apparatus is disclosed for cooling cones of molten glass by means of a solid metallic fin positioned between lateral rows of glass cones formed on the bottom of a bushing. The lateral fins in this patents are connected to a common header device through which cooling material such as water is circulated. The flat fins described provide heat transfer between the molten glass cones and the cooling liquid by using the thermal conductivity of the fins which while satisfactory is not the most efficient method of removing heat from the glass. These fins nevertheless have achieved a considerable degree of success in the art in that heat is removed from the cones of glass and dissipated to the common header where it is removed by the circulating cooling media passing therethrough. In U.S. Pat. No. 3,251,665, a hairpin cooler through which a cooling fluid is passed is positioned between the rows of cones in a fiber glass bushing operation to dissipate heat from the areas of the cones in a rapid manner to provide for even cone formation and adequate cooling of the glass fibers as they are emanating from the tip. Since the spacing between the tips is very small and the hairpins are of small diameter, however, difficulties are often encountered by impurities in the cooling fluid clogging the cooling fluid passages in the hairpin coolers.